High-current battery management system

ABSTRACT

An apparatus includes a microcontroller and isolation circuitry including multiple transistor-based switches arranged electrically in parallel to isolate a battery from a load source, wherein the battery is capable of providing high levels of current. The apparatus includes a first buss bar to which first pins of the multiple switches are connected, wherein the first buss bar is to be connected to the battery and a second buss bar to which second pins of the multiple switches are connected, wherein the second buss bar is to be connected to the load source. A microcontroller is programmed to control the multiple switches substantially simultaneously to isolate the battery from the load source upon detecting a predetermined condition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of PCT/US2014/40997, filedJun. 5, 2014, which claims the benefit of U.S. Provisional PatentApplication No. 61/836,233, filed Jun. 18, 2013, wherein the entiredisclosure of both applications are incorporated herein by thisreference.

BACKGROUND

1. Technical Field

The present disclosure relates generally to the management andprotection of batteries, and more specifically to a high-current batterymanagement system.

2. Description of Related Art

Lead Acid batteries are the common battery of choice for startinginternal combustion engines (ICE) vehicles. Lead acid batteries arerobust in that they can handle a fair number of charge-discharge cyclesand can operate in most non-extreme environmental temperature ranges.While they do degrade when over-discharged, the effect is not as drasticas other chemistries. Furthermore, lead-acid batteries are comparativelylow cost compared to other types of batteries.

However, other chemistries, such as lithium iron phosphate (LFP) haveadvantages over lead-acid batteries. Although there are severalchemistries that can have these advantages over lead-acid batteries, LFPis generally referred to herein by way of example only, and is not meantto be limiting. Batteries using other chemistries, such as LFP,typically consist of a battery pack made up of multiple cell banksarranged electrically in series to achieve the voltage output desired.Furthermore, a cell bank can consist of one cell, or multiple cellsarranged electrically in parallel to achieve the capacity level, orampere-hour (Ah), desired.

Advantages of using another chemistry, such as LFP, over lead-acidparticularly for starting ICE vehicles, include by way of example,substantially longer cycle lives, so the batteries can last much longer(around three to six times longer by most estimations). Batteries otherthan lead-acid batteries also have higher energy density, which allowsthe battery to be more compact than a lead-acid battery while stillmaintaining the same capacity (e.g., number of Ah). An LFP battery packcould be less than one half the size of a lead-acid battery and stillcontain the same amount of capacity.

The advantages of other-than-a-lead-acid battery also includes lessinternal resistance, so less capacity is needed to achieve the desiredcranking amperes (“amps”). A lead-acid battery with higher internalresistance requires that the battery bank be over-sized in order toachieve the necessary high surge current required to start an engine.One explanation for why this works is the surge current can bedistributed between cells connected electrically in parallel, reducingthe voltage drop as current passes over the internal resistanceaccording to Ohm's law (V=IR) over each individual cell's internalresistance. Another explanation is the fact that putting multiple cellsor banks in parallel reduces the overall effective internal resistanceof the power source according to the parallel impedance equation:

$\frac{1}{Z_{eq}} = {\frac{1}{Z_{1}} + \frac{1}{Z_{2}} + \cdots + {\frac{1}{Z_{n}}.}}$

The lower internal resistance of the LFP battery results in thecapability of the battery to provide the required high surge currentwith much less capacity. Because less capacity is needed, the volumetricsize of the battery can be reduced even further (approximately 50%-75%smaller). For example, because a lead-acid battery has much higherinternal resistance, a typical semi-truck may require a lead-acid bankwith a capacity of up to 280 Ah to achieve the necessary cranking ampsrequired to start the engine. This would require three to four lead-acidbatteries taking up approximately six to eight cubic feet. An LFPbattery with much lower internal resistance would only require acapacity of 46 Ah to start the same engine, and take up approximately acubic foot in comparison.

Other advantages of other-than-lead-acid batteries further include beingof lighter weight, making it easier to handle and less weight for thevehicle to carry. The lead-acid batteries for a semi-truck weighapproximately 200 pounds (lbs.) total while an LFP battery for startingthe same vehicle may weigh only about 20 lbs.

Also, an LFP battery includes no hydrogen off-gassing (so less chancefor explosion) and no sulphation, so no corrosion or corrosive leakage.Off-gassing, also referred to as outgassing, is the emission ofespecially noxious gases that is dissolved, trapped, frozen or absorbedin some material. Off-gassing can include sublimation and evaporationwhich are phase transitions of a substance into gas as well asdesorption, seepage from cracks or internal volumes and gaseous productsof slow chemical reactions. Sulphation is the normal movement of thesulfate radical SO4, from the sulfuric acid electrolyte H2SO4, to thebattery plates during the discharge and re-charging cycle of arechargeable battery.

An LFP battery, however, is not as robust as a lead-acid battery when itcomes to over-discharging or overheating. Additionally, lower internalresistance and the habit to have a smaller capacity battery also createsboth a safety concern as well as a need to protect and optimize theoperational life of the battery.

As mentioned above, today's lead-acid battery banks used for starting asemi-truck are over-sized in order to achieve the desired cranking amps.This results in a large amount of excess capacity in the battery bank.Because LFP requires less capacity to achieve needed cranking amps, LFPbatteries have considerably less excess capacity available for otherthings. For example, it is common for drivers to turn off their engineswhile stopping for rest, yet continue to use running lights, cab lights,fans, radios and other appliances. Because the lead-acid battery bankcontains a large amount of excess capacity, it can provide this powerfor a certain length of time. However, because the LFP battery has muchless capacity, there is much less excess capacity to use for such loads.If the driver were to use the same appliances, they would increase therisk of running down the battery and over-discharging it and increasingthe likelihood of a dead battery. Once over-discharged, an LFP batterydegrades much faster than a lead-acid battery, reducing the operationallife to less than that of a lead-acid battery.

Additionally, if the battery system were to experience a short circuit,the effect would be even more catastrophic than if a lead-acid batterysystem short circuits. The lower internal resistance allows for highersurge currents that can cause much greater damage than seen in lead-acidbatteries. For example, if a cable were to wear through its protectivesheathing and contact any metal on the truck, such as the frame or otherwiring, the entire battery system could instantaneously become red hotand the metals reach their melting point. The LFP battery could alsobegin to overheat at a rate much higher and to temperatures much higherthan in lead-acid batteries. Typically, the result would lead to a firein the vehicle, either from the battery itself bursting into flames, orother parts of the vehicles become overheated and combusting.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be understood more fully from the detaileddescription given below and from the accompanying drawings of variousembodiments of the disclosure. The drawings, however, should not betaken to limit the disclosure to the specific embodiments, but are forexplanation and understanding only.

FIG. 1 is a perspective view of a buss bar according to one embodiment.

FIG. 2 is a perspective view a circuit board with a bottom buss barattached, according to one embodiment.

FIG. 3 illustrates a battery management system (BMS) assembly as in FIG.2, with subarrays of metal-oxide semiconductor field-effect transistors(MOSFETs) and a top buss bar attached, according to one embodiment.

FIG. 4 illustrates a BMS assembly as in FIG. 3, but with bottom and topbuss bars according to another embodiment.

FIG. 5 illustrates a BMS assembly as in FIG. 3, with a heat tie added ontop of the MOSFET arrays according to one embodiment.

FIG. 6 illustrates an underside of the BMS assembly of FIG. 5 with metaloxide varistors (MOVs) and cell balancing circuitry, according to oneembodiment.

FIG. 7 is a block diagram of circuitry of a battery management system(BMS) located at least in part on the circuit board of FIGS. 2-6,according to one embodiment.

FIG. 8 is a circuit diagram of a MOSFET array attached between the topand bottom buss bars of FIGS. 1-6, according to one embodiment.

FIG. 9 is a circuit diagram of the MOSFET switching driver of thebattery management system of FIG. 7, according to one embodiment.

FIG. 10 is a circuit diagram of the surge detection circuit of thebattery management system of FIG. 7, according to one embodiment.

FIG. 11 is a circuit diagram of the surge measuring circuit of thebattery management system of FIG. 7, according to one embodiment.

FIG. 12 is a circuit diagram of the buss bar temperature sensor of thebattery management system of FIG. 7, according to one embodiment.

FIG. 13 is a circuit diagram of the cell bank voltage sensor of thebattery management system of FIG. 7, according to one embodiment.

FIG. 14 is a circuit diagram of a voltage divider that measures thecharge of an entire battery bank (e.g., cell pack) of the batterymanagement system of FIG. 7, according to one embodiment.

FIG. 15 is a circuit diagram of charge shunt circuitry of the batterymanagement system of FIG. 7, according to one embodiment.

DESCRIPTION OF EMBODIMENTS

For safety reasons, a battery management system (BMS) can protect thebattery from a short circuit or overheating by isolating the batteryfrom the load source. Additionally, in order to optimize the batterylife, the BMS can also detect a low voltage and isolate the battery toprevent the battery from being over-discharged. Current LFP batteriesfor starting vehicles do not have such a BMS that performs thisprotection and isolation, which are therefore not available to averageconsumers.

The BMS can be coupled to a battery cell pack such that the BMS residesin a single enclosure, generally referred to as a battery. “Cell pack”is one or more cell banks connected in series to achieve a desiredvoltage output. A cell bank is one or more cells connected in parallelto achieve a desired capacity. In the alternative, the BMS can beexternal to the battery in its own independent enclosure and connectedto the internal battery cell pack from the outside of the battery. Thislater configuration can be useful in aftermarket applications with abattery that was manufactured with no BMS. In either case, the BMS canbe connected in line at the negative terminal of the battery such thatthe BMS can control the return current to the battery and shut off powerfrom the battery, if necessary.

One challenge with creating a BMS for this scenario is the ability tocut a high current. A vehicle, such as a large semi-truck, can drawaround 400 amps while turning over the engine. However, there is amomentary spike in the current draw when the ignition is initiallyattempted. This current spike can reach as high as 2,500 amps, anextremely high current. This means the BMS should be able to allow atleast this much current to pass for a specified period of time withoutshutting off, to allow the vehicle to start properly. When an unexpectedhigh current is detected and determined to be outside of specified safeoperating ranges, the BMS is to cut the current at this very high level.Shutting off a high current like this is normally achieved withmechanical relays or insulated-gate bipolar transistors (IGBTs). Thesemechanical relays and IGBTs, however, are expensive and bulky, making itdifficult to fit the battery configured with mechanical relays or IGBTsinto the same size compartment as a standard vehicle starting battery.Use of mechanical relays or IGBTs also increases cost beyond pricescomparable to existing vehicle starting batteries.

Using a plurality of solid state semiconductor, transistor-basedswitches arranged electrically in parallel in a BMS is a less expensiveand a compact alternative. These transistor-based switches can include,for example, bipolar junction transistors (BJTs), metal-oxidesemiconductor field-effect transistors (MOSFETs), junction field-effecttransistors (J-FETs), meta-semiconductor field-effect transistors(MESFETs), or modulated-doping field-effect transistors ormodulation-doped field—effect transistors (MODFETs), and the like. Forease of explanation. the present disclosure will sometimes refer to allof these as “switches.”

Transistor-based switches, and particularly MOSFETs, are commonly usedin low current situations such as cellphones, laptops and other portablerechargeable devices (on the order of milliamps). Switches such asMOSFETs are significantly less expensive and less bulky than mechanicalrelays or IGBTs. However, MOSFETs are not available that can handlecurrents in the thousands of amps, and in these situations, designersusually employ electromechanical relays or IGBTs, which are designed forhigher power applications. In one embodiment, MOSFET-based switches aresignificantly less expensive, and less bulky, and by using an array oftransistor-based switches connected electrically in parallel it ispossible to handle high current situations when the current load can bedistributed and shared properly. For example, to use MOSFET-basedswitches in high current applications, the MOSFETs are to be protectedfrom overloading so that the MOSFETs can reliably be used to isolate thebattery from the system, as will be described in more detail.

Unfortunately, when transistor-based switches such as MOSFETS aremanufactured, each batch of the switches has a different Vgs (gate tosource voltage) or turn on voltage. Matching switches from the samebatch is only achievable during the silicon wafer manufacturing processand ensuring that switches are selected from the same batch is difficultand costly and therefore not a preferred option. The difference in turnon times between batches can only be slight (measured in nanoseconds andeven picoseconds), but is significant enough to make it difficult toswitch the switches on/off at the same time. This time difference cancause the faster switch in the array to carry the entire load and burnup.

By maintaining turn on times that are as close to the same as possibleamong all the switches in the array, the switches can distribute thecurrent simultaneously when cutting the current. Maintaining a similarturn on voltage across the array of switches is difficult but manageableif approached differently from common practices and recommendations forutilizing switches, as will be explained.

Additionally, when starting a vehicle with an electric starter motor, avery large inductive load is put on the battery that requires highcurrent. Suddenly switching the current off with this very largeinductive load creates a very fast and very large voltage spike(measured in kilovolts (kV)) that can overload the transistor-basedswitches, causing them to burst. If the inductive current is kept at orbelow recommended operating currents, the transistor-based switches canhandle them fine without overheating, provided the proper thermal heatsinking is used. While transistor-based switches are sensitive toovercurrent and overvoltage conditions, transistor-based switches can beemployed in a BMS as disclosed herein when these conditions are properlycontrolled.

In one embodiment, a rechargeable battery system of the presentdisclosure includes a battery pack and a battery management system(BMS). The battery pack has rechargeable battery cells that areconnected in a way that allows the battery cells to be discharged whenthe battery system is in operation. The BMS is connected to the batteryto allow data gathering from the battery, and to provide selectiveisolation between the battery and a load source. The BMS can beconfigured to perform cell balancing within the battery bank. Cellbalancing allows each of the rechargeable battery cells to be maintainedin a similar electrical state.

In still other embodiments, the BMS can include isolation circuitry. Theisolation circuitry can be configured to electrically isolate thebattery when a threatening electrical system event, for example a shortcircuit, is detected within or even outside of the battery system. Forexample, a battery system is designed with a battery pack containingrechargeable battery banks and cells, and a BMS can be connected to thebattery pack.

For example, a BMS can include isolation circuitry including multiple,transistor-based switches arranged electrically in parallel to isolate abattery from a load source, wherein the battery is capable of providinghigh levels of current of at least 400 amperes. The BMS can furtherinclude a switching driver circuit operatively coupled to the isolationcircuitry such as to switch off the multiple switches simultaneously.The BMS can further include a microcontroller operatively coupled to theswitching driver circuit and configured to direct the switching drivercircuit to turn off the multiple switches responsive to detecting apredetermined condition

In one embodiment, the microcontroller directs the switching drivercircuit to switch off the multiple switches at substantially the sametime, and other circuit design techniques can be used to synchronize thetiming of turning the multiple switches on and off. The structure andprogrammed control provide this timing in order to distribute the loadevenly, to prevent damage caused by overvoltage, as will be discussed inmore detail.

In another embodiment, a BMS can include isolation circuitry includingmultiple, transistor-based switches arranged electrically in parallel toisolate a battery from a load source, wherein the battery is capable ofproviding high levels of current. The BMS can further include a firstbuss bar to which first pins of the multiple switches are connected,wherein the first buss bar is to be connected to the battery and asecond buss bar to which second pins of the multiple switches areconnected, wherein the second buss bar is to be connected to the loadsource. A microcontroller of the BMS can be programmed to control themultiple switches substantially simultaneously responsive to detecting apredetermined condition. For example, the microcontroller can receive asignal indicating any number of conditions, such as a short circuit inthe load source, overheating of the battery, overheating of theisolation circuitry, a low-voltage threshold of the battery, or auser-initiated shut off, among other as will be discussed.

In yet another embodiment, the BMS can further include a surge detectioncircuit including an operation amplifier to detect a surge in current bymeasuring a voltage difference between source and drain of a subset ofthe multiple switches. The BMS can further include a surge measuringcircuit to measure a magnetic field and to determine a current level ofthe surge in current. The microcontroller can be operatively coupled tothe surge detection circuit and the surge measuring circuit, wherein themicrocontroller is to: receive a first signal from the surge detectioncircuit, wherein the first signal is indicative of detecting the surgein current; turn on the surge measuring circuit responsive to thesignal; receive the current level of the surge from the currentmeasuring circuit; and send a second signal to switch off the multipleswitches responsive to determining that the current level is above apre-defined threshold current level indicating a short circuit. In oneembodiment, the surge measuring circuit includes a Hall Effect sensorattached to a circuit board with which to measure the magnetic field.

These and other features will now be explained in more detail that helpto prevent individual transistor-based switches from overcurrent andovervoltage conditions by synchronizing turn on times, and othersolutions that reduce the effects of voltage spikes, short circuits andthe like.

FIG. 1 is a perspective view of a buss bar 100 according to oneembodiment. The buss bar 100 can include a single conductive path (ortwo co-conductive paths) as in FIG. 4, or as in FIG. 1, a firstconductive path 102 a and a second conductive path 102 b that connect toeach other. As shown in FIG. 1, the first conductive path 102 a and thesecond conductive path 102 b can form a horseshoe shape, although othershapes are envisioned that likewise provide two conductive paths, suchas a V-shape, a square or rectangular shape and the like. The buss bar100 can also include a number of apertures through which to connect thebuss bar 100 to a battery pack or to a load source, e.g., a vehicle whenthe battery pack (or battery) is to turn on and power the vehicle. Inthe description herein, battery pack and battery can be usedinterchangeably to refer to a source of stored power deliverable ascurrent to a load source. In some cases, however, the term battery canbe considered to include a battery pack made up of banks of storagecells.

FIG. 2 is a perspective view a circuit board 200 with a bottom buss bar100 a attached to the circuit board 200, according to one embodiment. Anumber of electrical and sensing components can be attached to thecircuit board 200 that perform or help perform a number of isolation andprotection functions as well as communication and monitoring functions.For example, a first metal trace 202 a and a second metal trace 202 b(one for each sub-array of switches that is arranged along eachconductive path 102 a and 102 b, respectively) can be formed on thecircuit board 200. Additional components, which will be discussed inmore detail with reference to FIGS. 7-14, include but are not limited toa switching driver circuit 204, a microcontroller 206, Hall Effectsensors 210 a and 210 b, a satellite board connector 214, a data port216 (e.g., a universal serial bus (USB) connector), wireless circuitry220, global positioning system (GPS) circuitry 224, a reset button 228to allow the user to reconnect the battery to the system ifpre-determined requirements are met, a light emitting diode (LED) (orother type of) display 230 to provide status indications andinstructions to an operator, and a temperature sensor 234.

The satellite board connector 214, the data port 216, the wirelesscircuitry 220 and the GPS circuitry 224 can also act as a communicationinterface in various embodiments that enables communications via one ormore communications networks. A communication network can include wirednetworks, wireless networks, or combinations thereof. Such acommunication interface over the communications network(s) can enablecommunications via any number of communication standards, such as802.11, 802.17, 802.20, WiMax, 3G, 4G, long term evolution (LTE) orother cellular telephone or communication standards.

FIG. 3 illustrates a battery management system (BMS) assembly 300 as inFIG. 2, further illustrating an array 304 of solid state semiconductorswitches such as multiple transistor-based switches 302, which sometimesare referred to as switches 302 for ease of explanation. The array 304of switches 302 can further be broken down into two subarrays ofswitches. These two subarrays can include a first subarray 308 a and asecond subarray 308 b of transistor-based switches 302 connected to thecircuit board 200 and between the bottom buss bar 100 a and a second (ortop) buss bar 100 b. In a typical configuration, the bottom buss bar 100a is to be connected to the battery and the top buss bar 100 b is to beconnected to the load source, although these can be switched in anotherembodiment. In one embodiment, the first subarray 308 a and the secondsubarray 308 b each include an equal number of switches, thus balancingthe current load on the first switches closest to the load source acrossmultiple subarrays of switches.

In other words, when the current travels through a buss bar, the currentarrives at the first switch on the buss bar (the one closest to the loadsource) sooner than it arrives at the last switch in the line. Althoughseemingly negligible, this time difference can cause the first switch tooverload and burst before the current is equalized across the array ofswitches in high current applications. Accordingly, this time differencecan be reduced by arranging multiple subarrays 308 a and 308 b of equalnumbers of electrically parallel switches 302 along each of the multipleelectrically parallel conductive paths of the buss bars. The relief toeach first switch of each subarray is proportional to the number ofsubarrays of switches arranged in parallel, so it is envisioned thatmore than two subarrays 308 a and 308 b could be employed.

With further reference to FIG. 3, the switches 302 of the first subarray308 a can be arranged in a line along an edge of the first conductivepath 102 a and of the second subarray 308 b can be arranged in a linealong an edge of the second conductive path 102 b. In one embodiment,the edges can oppose each other so that at least the first switch fromeach of the two different subarrays are located equidistant from thebattery (along the bottom buss bar 100 b) and are located equidistantfrom the load source (along the top buss bar 100 a). In this way, firstcurrent moving between the first subarray 308 a and the battery canarrive at substantially the same time as second current moving betweenthe second subarray 308 b and the battery. Similarly, third currentmoving between the first subarray and the load source can arrive atsubstantially the same time as fourth current moving between the secondsubarray 308 b and the load source. This works to further synchronizethe time at which the switches are loaded. This method alone(synchronizing the time at which the current reaches the switches),however, may not necessarily be enough to protect the switches fromoverloading, particularly in ultra-high current situations.

FIG. 4 illustrates a BMS assembly 400 as in FIG. 3, but with a bottombuss bar 400 a and a top buss bar 400 b according to another embodiment.In this embodiment, each buss bar 400 a and 400 b can be considered tohave a single conductive path, or two co-conductive paths. Theco-conductive paths of each buss bar 400 a and 400 b are stillconnected, however, and provide opposing edges along which to positionthe first subarray 308 a and the second subarray 308 b of switches 302,respectively.

In one embodiment, the source pin of each transistor-based 302 switch isconnected to the bottom buss bar 100 a or 400 a and the drain pin ofeach switch 302 is connected to the top buss bar 100 b or 400 b. Inanother embodiment, these connections are switched. The circuit board200 can include holes through which each source pin can pass to connectto the bottom buss bar 100 a located beneath the circuit board 200. Inone embodiment, the first pins of the switches are of equal length andthe second pins of the switches are equal length, to further synchronizethe timing of current arriving at the switches 302 of respectivesubarrays 308 a and 308 b.

In one embodiment, the metal traces 202 a and 202 b (of FIG. 2 and nowhidden in FIG. 3) can connect gates of the transistor-based switches 302to a switching driver circuit 204 and be electrically equidistant fromthe switching driver circuit 204, which controls switching thesemiconductor switches on and off as directed by a microcontroller 206(see also FIG. 7). This is referred to as trace matching, and can betuned such that the arrival of an on/off signal at any two switches 302is as close to the exact moment as possible, where even a few nanosecondcan be too much time. This is the case particularly with high current,where a difference of too much time could cause one switch to quicklyconduct too much current (an overcurrent situation), overloading theswitch and causing it to burst before other switches in the array candivert some of that current. However, synchronizing the timing of thesignal with metal tracing alone is not necessarily enough to protect theswitches from overcurrent.

FIG. 5 illustrates a BMS assembly 500 as in FIG. 3, with a heat tie 502added on top of the subarrays 308 a and 308 b of transistor-basedswitches 302 according to one embodiment. The heat tie 502, alsoreferred to as a heat conducting bar, can be thermally coupled to theswitches to equalize the temperature across the switches 302. In oneembodiment the heat tie 502 is made of an appropriately-sized heatconducting material meant to equalize heat across the heat tie and thusacross the switches. Equalizing the temperature across the switches 302allows the temperature of each switch to be as close to the same as thetemperature of any other switch. This is beneficial because temperatureimpacts the turn on voltage (V_(t)), which can be expressed as:

$V_{T} = {V_{FB} + {2\varphi_{F}} + {\frac{\sqrt{2\; s_{5}{{qN}_{a}\left( {{2\varphi_{F}} + V_{SB}} \right.}}}{C_{ox}}.}}$

The φ_(F) parameter can be significantly affected by temperature andwhich represents half the surface potential of the switches. Theequation for φF, expressed as

φF ₌(kT/q)ln(N _(A) /N _(i))

shows the dependency on temperature T. As T increases, φ_(F) alsoincreases, causing the turn on voltage to increase. This means that ifone switch is cooler than another, then the one switch will turn on morequickly as the turn-on signal (gate voltage) does not have to rise to ashigh of a value to overcome the turn-on voltage. Accordingly,temperature differences between the switches affect the ability of theBMS to turn on or off the switches at substantially the same time, andavoid an overcurrent condition on any individual switch that could causethe switch to burn out. Only equalizing the temperature across all theswitches, however, may not necessarily protect against all overcurrentsituations.

FIG. 6 illustrates an underside of the BMS assembly 500 of FIG. 5 withmetal oxide varistors (MOVs) 607 a and 607 b and bank balancingcircuitry 603, according to one embodiment. The bank balancing circuitry603 will be discussed in more detail with reference to FIG. 7. Whereslower switching alone may not reduce the voltage spike enough toprotect the switches 302 from overvoltage and damage, any remainingvoltage spikes can be shunted away from the switches 302 to furtherprotect the switches from damage.

The MOVs 607 a and 607 b can be used to provide voltage suppression toprotect the switches 302 from overvoltage by shunting the current causedby high voltages away from the switches 302. An MOV is a variableresistor, which increases in resistance at low voltages and decreases inresistance at high voltages. By placing the MOV electrically in parallelwith the switches, the high resistance during normal operation will notshunt a significant amount of current away from the switches. However,because resistance of the MOV decreases at high voltages, a voltagespike can effectively turn the MOV into a short circuit and shunt thecurrent away from the switches 302 so as not to overload the switches.Using only MOVs to suppress voltage spikes may not necessarily besufficient to protect the switches from overvoltage situations. Forexample, combining the MOVs 607 a and 607 b with slow switching of theswitches 302 can be used to more reliably protect the switches fromovervoltage.

FIG. 7 is a block diagram of circuitry of a battery management system(BMS) 700 located at least in part on the circuit board of FIGS. 2-6,according to one embodiment. Additional or fewer components arecontemplated in additional embodiments, and as will be apparent herein.The BMS 700 can include the MOSFET subarrays 308 a and 308 a andattached bottom buss bar 100 a or 400 a and top buss bar 100 b or 400 bthat can be coupled between a battery 705 and a load 715. The battery705 can include multiple cell banks, including in the illustratedembodiment, Bank_1, Bank_2, Bank_3 and Bank_4, to increase voltageoutput. A more-detailed circuit diagram of the array 304 of switches302, the bottom buss bar 100 a or 400 a, and the top buss bar 100 b or400 b is shown in FIG. 8, according to one embodiment.

The microcontroller 209 can receive sensor signals and other informationwith which to manage and monitor the battery and other potentiallyunsafe conditions. Voltage and current levels along with otherparameters and features can be stored in a memory 207 for laterretrieval by the microcontroller 209. The memory 207 can becomputer-readable media. A “computer-readable medium,”“computer-readable storage medium,” “machine readable medium,”“propagated-signal medium,” and/or “signal-bearing medium” can includeany device that includes, stores, communicates, propagates, ortransports software for use by or in connection with an instructionexecutable system, apparatus, or device. The machine-readable medium canselectively be, but not limited to, an electronic, magnetic, optical,electromagnetic, infrared, or semiconductor system, apparatus, device,or propagation medium.

Accordingly, the BMS 700 and methods disclosed herein can be realized inhardware, software, including firmware, or a combination of hardware andsoftware. The BMS 700 and methods can be realized in a centralizedfashion in at least one BMS or in a distributed fashion where differentelements are spread across several interconnected BMSs. Any kind ofcomputer system or other apparatus adapted for carrying out the methodsdescribed herein is suited. The BMS 700 and methods can also be embeddedin a computer program product, which includes all the features enablingthe implementation of the operations described herein and which, whenloaded in a BMS of sufficient capability, is able to carry out theseoperations. Computer program in the present context means anyexpression, in any language, code or notation, of a set of instructionsintended to cause a BMS having an information processing capability toperform a particular function, either directly or after either or bothof the following: a) conversion to another language, code or notation;b) reproduction in a different material form.

With continued reference to FIG. 7, the BMS 700 can further include theswitching driver circuit 204 operatively coupled between themicrocontroller 209 and the switches 302 of the subarrays 308 a and 308b. A more-detailed circuit diagram of the switching driver circuit 204is shown in FIG. 9, according to one embodiment. An on/off signal fromthe microcontroller 209 comes into the switching driver circuit 204 anda battery on/off signal is output from the switching driver circuit 204,to turn off the switches 302 as discussed herein. The switching drivercircuit 204 can amplify the signal from the microcontroller 209 and slowthe switching speeds to reduce current spikes.

For example, when suddenly switching off high currents with a largeinductive load, as is done with a high-current battery for example, thebattery can experience very large voltage spikes (in the kV range).These spikes can overload the switches 302 and cause the switches toburst. The size of the voltage spike depends on the equation for thevoltage across an inductor, expressed as:

$\upsilon = {{\frac{}{t}({Li})} = {L{\frac{i}{t}.}}}$

which states that the voltage is equal to the rate of change of thecurrent times the inductance. The faster the current changes, the higherthe voltage spike.

To reduce the rate of change of current (when the switches are switchedoff), and thereby reduce overvoltage due the voltage spike, switchingcircuitry in the switching driver circuit 204 can be designed orprogrammed to turn the switches 302 on and off at speeds as slow aspossible, to reduce the change in current over time without exceedingthe maximum allowable power dissipation caused by switching (switchingcauses the highest power dissipation in most types of transistorsincluding MOSFETS). In one embodiment, for example, component values ofa resistive-capacitive (RC) circuit of the switching driver circuit 204can be set to a specific rise time for the turn on/off signal. Thissetting is well below the manufacturers recommendations. It is commonlyheld that transistor-based switches such as MOSFETs should switch off asfast as possible, so switching as slow as possible is a counterintuitive approach. Only slowing the switching speed, however, may notnecessarily protect all of the switches from overvoltage due to voltagespikes.

The BMS 700 can further include a surge detection circuit 713 located onthe circuit board 200 and operatively coupled to the microcontroller 209to provide a first-stage surge detection. In one embodiment, the surgedetection circuit 713 also operates as a current sensing circuit. Amore-detailed circuit diagram of the surge detection circuit 713 isillustrated in FIG. 10, according to one embodiment. A dualoperational-amplifier (op-amp) circuit 1010 can send an I_SENSE_ONsignal to indicate to the microcontroller 209 to turn on a surgemeasuring circuit 710. The op-amp circuit 101 can provide initial,low-power current sensing by measuring a voltage difference betweensource and drain of a subarray of electrically parallel switches, e.g.,subarray 308 a and/or subarray 308 b, and calculating the current basedon the switches' specific voltage-current characteristics. Thecalculated current can be sent to the microcontroller 209 through theVdrain_G6 pin.

A digital-to-analog converter (ADC) 709 may be included to help convertthe current to a digital signal readable by the microcontroller 209. Indifferent embodiments, the ADC 709 can be integrated into themicrocontroller 709 (as shown) or into the surge detection circuit 713,or can be a stand-alone ADC 709 on the circuit board 200.

Upon detecting a sufficient surge in current, the I_SENSE_ON signal canalert the microcontroller that a current over a predetermined threshold(e.g., 10, 15 or 25 amps or the like) has been detected. Themicrocontroller 209 can then turn on Hall Effect sensors 210 a and 210 bto more accurately measure how much current the surge contains, to helpdistinguish between, for example, an engine start and a short circuit aswill be discussed in more detail.

For example, the BMS 700 can further include the surge measuring circuit710, which can include a left Hall Effect sensor 210 a and a right HallEffect sensor 210 b, attached to the circuit board 200 and operativelycoupled to the microcontroller 209. A more-detailed circuit diagram ofthe left Hall Effect sensor 210 a of the surge measuring circuit 710 isillustrated in FIG. 11, according to one embodiment. A Hall Effectvoltage (V_(hall)), which represents the magnitude of the magnetic fieldcreated by the buss bar current that is sensed, is output to themicrocontroller 209. The microcontroller 209 can then determine whetheror not the V_(hall) value is within operating ranges and takeappropriate action that may be necessary, such as switching off thetransistor-based switches 302.

The BMS 700 can further include the temperature sensor 234, locatablebetween the circuit board 200 (FIGS. 2-6) and at least one buss bar, andwhich is also operatively coupled to the microcontroller 209. Amore-detailed circuit diagram of the temperature sensor 234 isillustrated in FIG. 12, according to one embodiment. The buss bartemperature is output from the temperature sensor 234 to themicrocontroller 209.

The BMS 700 can further include the bank balancing circuitry 603 andcorresponding bank voltage sensors 703 operatively coupled between themicrocontroller 209 and the banks within the battery 705. Amore-detailed circuit diagram of the bank voltage sensors 703 isillustrated in FIG. 13, according to one embodiment. A voltage outputfor each bank of the battery 705 is sent to the microcontroller 209. Anexample voltage divider 1400 as illustrated in FIG. 14 can be used tomeasure a charge the entire battery pack, e.g., battery 705. Dividingthe voltage down to a lower voltage can allow the microcontroller 209 orthe ADC 709 to properly handle or operate on the lower voltages.

Furthermore, a more-detailed circuit diagram of the bank balancingcircuitry 603, with separate circuits 603 a, 603 b, 603 c and 603 d tobalance, respectively, Bank_1, Bank_2, Bank_3 and Bank_4 within thebattery 705 is illustrated in FIG. 15 according to embodiment. Eachbalancing circuit receives a corresponding bank control signal from themicrocontroller 209.

With it now possible to consistently protect the array 304 oftransistor-based switches from damage due to overcurrent or overvoltagesituations, the array 304 can be reliably used as an isolation circuit.A microcontroller 209 can be operatively coupled to the isolationcircuitry to control when current is allowed to pass and when it is cutoff, or in other words, when the battery should be connected to a loudsource (or other electrical system) and when it should be isolated fromthe load source. Voltage sensors, temperature sensors and other suchsensors or sensing devices that can detect an event and send a signal tothe microcontroller 209 can be used to help the microcontroller 209 knowwhen to allow current to pass though the battery 705, and whether to cutoff current through the battery due to an unsafe condition as defined bythe micro-controller's programming. In the case of a starter battery, weprotect against certain events that could create a dangerous situationor reduce the life of a battery as now explained in more detail withreference to FIGS. 1-15.

Measuring Current Surges and Detecting a Short Circuit

Current surges can be created in a number of ways. Some may be part ofnormal operation conditions, such as starting a vehicle, while othersare caused by an unsafe operating condition, such as a short circuit inthe system. These surges are to be detected and measured so as todetermine a current condition of an electrical system, and takefavorable action, if necessary. When the current surges, there is also alarge surge in the magnetic field of the buss bar 100. The Hall Effectsensors 210 a and 210 b can be used to detect this surge. The term “HallEffect” refers to a potential difference observed between the edges of aconducting strip carrying a longitudinal current when placed in amagnetic field perpendicular to the plane of the strip, which in thepresent disclosure is the plane of the buss bars 100 and 400.

In one embodiment, each Hall Effect sensor 210 a and 210 b is placednear the edge of a conducting path of the buss bar (e.g., of 102 a or102 b) where the magnetic field is strongest so the Hall Effect sensorscan be more effective. Each Hall Effect sensor can measure the currentin the conductive path. Each Hall Effect sensor then reports the currentto the microcontroller 209. The microcontroller 209 can then determinewhether or not a short-circuit condition exists by analyzing themagnitude and duration of the surge. If the surge satisfies theconditions for a short circuit, the microcontroller can signal theswitching driver circuit 204 to activate the isolation circuitry, andtherefore disconnect the battery 705 from the load 715.

Hall Effect sensors require a relatively large current (several mA) tofunction. If used continuously to monitor the current, the Hall Effectsensors 210 a and 210 b can drain the battery in a relativity shortamount of time. To prevent this, a low-power consuming method, such asthe op-amp-based amplifier in combination with the ADC 709 can be usedas the surge detection circuit 713 (FIGS. 7 and 10). This surgedetection circuit can also act as a current sensing circuit and canmonitor the relative current by measuring the voltage difference acrossthe drain and source of the electrically parallel array 304 of switches.While this method consumes very little power and can detect a surge incurrent, it cannot accurately measure the surge at high levels.

In one embodiment, the surge measuring circuit 710 remains off until themicrocontroller 209 signals the microcontroller 209 to turn on, therebysaving power. When the surge detection circuit 713 detects a surge, thesurge detection circuit 713 signals the microcontroller 209, which inturn directs the surge measuring circuit 710 to turn on. Themicrocontroller 209 can turn on the Hall Effect sensors 210 a and 210 bto measure the magnetic field, determine the current level, and reportback to the microcontroller 209. The microcontroller 209 can thendetermine (from its programming) whether the surge constitutes a shortcircuit and, therefore, whether the isolation circuitry is to beactivated. For example, a pre-defined threshold level of current can beset for a particularly-sized battery 705 or load 715 (or a certaincombination thereof) that is compared to the determined surge in currentto determine whether the surge constitutes a short circuit. In this way,the low-current consuming surge detection circuit 713 can save power byanticipating a potentially high current situation where the BMS 700might need to turn on the Hall-effect sensors to measure the surge incurrent. This approach allows for constant monitoring of current levelswithout draining the battery 705 and can be done quickly enough toisolate the battery 705 before a short circuit can cause significantdamage.

In many low-power current sensing circuits, a series resistor is usedfor current measurement by measuring the voltage across the resistor andcalculating the current using ohms law. In the present BMS 700, a seriesresistor may not be practical because of the very large currentspresent. Every conductor, however, has a resistance, although in somecases the resistance is small, it could be treated as a series resistor.The resistance of such a conductor can be measured using a very accuratedevice because the resistance is so small, so that determining a currentflow through the conductor can be performed at a proper granularity andwith accuracy.

Accordingly, the buss bar 100 a, 100 b, 400 a or 400 b can be consideredas a series resistor, and the current can be calculated by measuring thevoltage across the buss bar and using ohms law. In the present BMS 700,the measurement can be done with measurement circuitry including the ADC709, which the microcontroller 209 can use to measure an accuratevoltage across the buss bar. In one embodiment, the measurementcircuitry is integrated with or operatively coupled to themicrocontroller 209. Because the resistance is small and slightly variedwith each buss bar used as a conductor, the resistance is preferablymeasured in production during calibration and stored in the memory 207or other firmware, so as to be available to the microcontroller 209during operation. During operation, the microcontroller can determinethe current flowing through the switches 302, using Ohm's Law, from themeasured voltage and the stored resistance. The measurement circuitrycan also include a ranging circuit to supply the ADC 709 with thecorrect range of voltages that corresponds to the possible currentmagnitudes. In one embodiment, this ranging circuit can include an opamp, voltage divider, and overvoltage protection.

The resistance measurement circuitry (and/or the microcontroller 209)can also be programmed to distinguish between a high current surgesituation that occurs, for example, when starting a vehicle, and a highcurrent surge caused by an actual short circuit. The resistancemeasurement circuitry can do this by monitoring the time at which thecurrent surge (and a current surge of a particular threshold level) isat an expected level for starting a vehicle. When a short circuit isdetected, the switching driver circuit 204 is directed to send a signalto the switch gates to turn off the switches 302 before damage canoccur, and prevents the switches from being turned on until theshort-circuit is removed.

Voltage Measurement and Low Voltage Detection

A lithium iron phosphate (LFP) cell or cell bank produces an outputvoltage of approximately 3.3 volts. This output voltage commonly has anarrow range of safe operating voltages, approximately between three (3)and four (4) volts. Operating outside of this operating voltage rangewill cause the cells to degrade to the point where they will no longerhold a charge and become unusable. The BMS can, therefore, detect whenthe voltage is outside of the optimal range and isolate the battery frombeing overcharged or over discharged. The voltage of each bank of cellscan be monitored independently as well as the entire pack voltagecollectively, to be able to pinpoint individual banks that can beovercharged or over discharged. An ADC can be used to detect voltagelevels.

As the voltage drops while the battery 705 is being discharged, themicrocontroller 209 can be programmed to recognize where the voltage isin relation to the operating range. Additionally, multiplepre-programmed or preset lockouts can be programmed to desired voltagethresholds. When the microcontroller 209 determines that one of thesethresholds has been met, the microcontroller can direct the isolationcircuitry to activate. The ability to program these presets isadvantageous because it allows for quick and easy custom configurationsfor diverse applications such as use of different chemistries,automotive and marine engine starting, auxiliary power units, emergencypower storage, and others. When a voltage threshold has been met, asignal can be sent to activate the isolation circuitry until a specifiedcondition is met.

The most common presets can include, but not be limited to:

Reserve Voltage:

Reserve voltage is when the voltage level of the battery 705 drops to adangerously low level but not yet outside of the safe operating range.This is set to reserve enough battery capacity to start the vehiclewithout dropping below the operating voltage range. The reserve voltagecan be reset manually (via the reset button 228) or wirelessly, forexample, by a mobile device.

Low Voltage Lockout:

A low voltage lockout can be reached when the voltage level of thebattery 705 has dropped below the operating voltage. The battery canremain at this low level for long periods without degradation of thecells and this level is specific to each type of battery chemistry. Themicrocontroller 209 can be programmed with a low voltage lockout toallow reset only when the battery is recharged to a level within thesafe operating range. The reset can happen manually through the restbutton 228, a wireless signal or the like. The microcontroller 209 canalso be programmed to automatically reset the battery 705 when thebattery 705 is safely within the safe operating range.

Critical Voltage:

At and below a critical voltage level, the battery 705 can still beusable, but cell degradation can start to occur, reducing theoperational life of the battery. This level is specific to each type ofbattery chemistry. The longer the battery stays below this level and thelower the voltage gets, the greater the degradation that occurs. Themicrocontroller 209 can track the length of time the voltage stays inthis state. The microcontroller 209 can be programmed with this criticalvoltage and only allow reset when the battery is recharged to operatinglevels.

Temperature Monitoring of the BMS

A temperature sensor 234 (or thermal sensor) located near or against abuss bar 100 a, 400 a or 100 b, 400 b can be used to monitor temperaturelevels of the BMS. The temperature sensor relays the temperature to themicrocontroller 209. In one embodiment, when a specified hightemperature is reached, the microcontroller 209 can direct the switchingdriver circuit 204 to send a signal to the transistor-based switch gatesto turn off the switches 302 before damage can occur, and prevents theswitches from being turned on until the temperature has returned to aspecified level within the safe operating range.

Temperature Monitoring of Banks of Cells

A thermal sensor (not shown), such as a thermistor, can be located in oraround each cell pack (or bank of the battery 205) when the cell pack ismanufactured. In one embodiment, the thermal sensor is located centrallyin the bank as that is where heat will concentrate the most. The thermalsensor can then relay the temperature of the cell pack to themicrocontroller 209, allowing the temperature of the cell pack to bemonitored to determine whether the cell pack is within acceptableoperating temperature ranges. When a specified high temperature isreached, the switching driver circuit 204 can send a signal to thetransistor-based switch gates to switch off the switches 302 beforedamage can occur, and prevent the switches from being turned on untilthe temperature has returned to safe operating levels.

Current Leakage Detection

The BMS 700 can detect when there is a low amount of current being drawnfrom the battery while the engine is not running (for example, when thelights are left on, etc.). In this situation, the BMS can alert the userand even be programmed to isolate the battery so further leakage cannotoccur. It can determine whether or not the engine is on by monitoringthe charge current from the alternator and use this information todetect a slow steady power draw on the battery when the engine is notrunning.

Cell Bank Balancing

When the output voltage of the cells of a battery bank is outside of theoperating range, cell degradation starts to occur. It is advantageousthat each cell bank be fully charged. However, cells can charge anddischarge at different rates, resulting in different charge levels ineach bank. During the charging process, some cells reach full chargebefore others and begin to overcharge. Overcharging can start to degradethe battery cells. It is therefore advantageous during charging todetect when the voltage reaches its optimum, fully-charged level and toprotect each cell bank from being overcharged or left undercharged. Cellbalancing is beneficial because it prevents unbalanced cell banks thatlead to overcharging of the bank and damage to cells, as well aspreventing inability for the battery to be fully charged.

The BMS 700 can use either passive or active cell balancing. Withpassive cell balancing, the bank balancing circuitry 603 includes chargeshunt circuitry to ensure the cells in the battery 705 are chargeduniformly. When battery cells are discharged, the cells do not alwaysdischarge uniformly. This can cause an imbalance when recharged. Toprevent an imbalance in charging, the cell balancing circuitry 603 canbe used to redirect the current from a fully charged bank of cells to abank of resistors that dissipate the charge to ground until all of thecell banks have reached full charge. A bank voltage sensor 703 can beused to monitor the cells of the battery 705 and a voltage dividercircuit 1400 (FIG. 14) can be used to create a measurable signal for theADC and measure the charge level of each cell bank.

The BMS 700 can alternatively, or additionally, have active balancing asa part of the cell balancing circuity 603. Active balancing redirectsthe current from a fully charged cell bank to another bank that isn'tfully charged and continues doing this until all banks are fullycharged. This is advantageous because the battery can be fully chargedusing less power and in less time.

Additionally, the BMS 700 has features programmed into its firmware,e.g., on the circuit board 200 and within the microcontroller 209 andother components, to provide functionality that does not exist withcurrent starter batteries as detailed below.

Data Logging

Tracking Health Indicators:

Replacement of batteries is typically done either when the battery nolonger holds a charge (a dead battery) or on a schedule. The health of alead-acid battery is difficult to determine and therefore when thebattery should be replaced cannot be accurately determined. A deadbattery can cause considerable inconvenience and cost, especially in thetrucking industry. Efforts are made, therefore, to prevent the batteryfrom failing in the field. A schedule can be created that calls forchanging the battery well before its possible end of life, regardless ofhow much life can be left. In most instances, there is considerable lifeleft in the battery, but because it is indiscernible how much, thetrucking industry (among other industries) prefers to remove doubt andreplace the battery. This has a considerable cost that the industry hasno choice but to accept. A lithium battery that includes or is managedby a BMS can be diagnosed and its operational life can be determinedwith a certain degree of accuracy, thereby optimizing the use of thebattery. Tracked health indicators can be reported back to the user tosignal when it is time to replace a battery, e.g., through the display230.

Transistor-Based Switch Degradation:

Switching transistor-based switches 302 such as MOSFETs at high currentscause the switches to breakdown over time, although tests show theselast for at least hundreds of short circuit events using the methodsdescribed in this application. When a switch in a particular subarrayfails, the load decreases in that subarray. If the switches in thatsubarray continue to fail, the load will continue to decrease. If aswitch in another subarray fails, the load balance will fluctuate. TheBMS 700 can detect the breakdown (degradation) of the switches bymonitoring these changes in load balances between the individualconductor paths (with the different subarrays of the buss bars) usingthe current sensing capability of the surge detection circuit 713 todetermine current levels in each conductive path. The microcontroller209 can receive the current levels in each conductive path and comparethe two current levels. When a difference between the two current levelsare beyond a pre-defined threshold amount, for example 1, 2 or 5 amps(or some other threshold), the microcontroller 209 can generate an alertindicative of a certain level of switch degradation, e.g., an audiblealert or a visual alert through the display 230.

Battery Cell Degradation:

As a battery cell reaches its cycle life limit (or when it is usedoutside of its operating conditions), the battery cell will start tolose its ability to hold a charge. The charging holding capability ofeach cell bank can be monitored to detect when this degradation startsto occur or detect a level of cell degradation. Determining celldegradation in this way can be performed by one or a combination ofmethods, as follows:

(1) In one embodiment, the ADC 709 can be used to measure the cellvoltage and determine the number of charge cycles the battery hasexperienced (which is limited) by counting the times the voltage hasfluctuated from high to low and back. Beyond a certain number of chargecycles, the battery 705 begins to degrade.

(2) In another embodiment, the microcontroller 209 can monitor the cellbanks of the battery 705 for a critical voltage level and for an amountof time spent at the critical voltage level. The critical low voltagelevel is a low voltage level that can be defined for banks of batteriesdepending on type and size of battery. The microcontroller 209 canmonitor and determine a length of time a battery bank has been atcritical voltage levels to detect cell degradation. The longer thebattery has been kept at critical levels, the more degradation thatoccurs. This degradation occurs even if the battery is not being used.Understanding this information can help to determine whether the batteryhas been maintained properly over its life.

(3) The microcontroller 209 can also track a number of times the battery705 has been charged and discharged, including how often the battery hasbeen discharged in a normal fashion (for example in starting thevehicle) and how often the battery 705 has been deep cycled (e.g.,running other things that bring the charge down further than with just aregular vehicle start). Based on this (and potentially other)information, the microcontroller 209 can determine not only if batterycapacity is decreasing over time, but also whether there is a problemwith the charging system (e.g., an alternator) and whether an electricalsystem is using more or less power than normal (e.g., lights burned outor short circuits present).

The microcontroller 209 can then generate an alert (such as an audiblealert of a visual alert on the display 230, or a data download to asmart phone or another computer) indicative of degradation of a bank ofcell in the battery 705, responsive to detecting one of the above threeconditions. In this way, the BMS 700 can more accurately detect batterycell degradation and timing of battery replacement.

Event Logging:

As events such as these occur, the events can be recorded and reportedback to the user to help understand how the battery is being used andhow it is performing. Examples of such events include, but are notlimited to: (1) short circuits; (2) high temperature levels; (3) lowvoltage levels; and (4) time spent at critical voltage, for example.

Communications & Control

Additional features allow for communication with and external control ofthe BMS 700 using either wired (such as a USB port) or wireless methods(such as Wifi, Bluetooth, GSM and other technologies that can transmitto a remote location) or a combination of both. Components for thesefeatures can be placed on the circuit board 200 or on a satellite boardconnectable to the circuit board 200 through the satellite boardconnector 214. The ability to monitor and control a vehicle batterywhile it is installed in the vehicle provides a powerful advantage. Thisability enables the user to accurately diagnose problems as well asidentify potential problems before the problems occur. When themicrocontroller 209 receives signals and reports from the variousmethods of monitoring the battery pack as described herein, themicrocontroller 209 can record that information forming a batteryhistory and saving that history for later retrieval.

The BMS 700 further provides for downloading or transmission of loggeddata (health indicators and events, for example) from the BMS 700 to auser, who can be at a remote location through wired or wireless means asdisclosed herein. Such data communication allows the tracking of batteryusage history. When the battery 705 is operational, the data can be usedto diagnose the health of the battery and determining the optimal timefor replacement. In the case of a failed battery, the data can be usedto determine the cause of the failure. And, during testing, the data canbe used to see the performance of the BMS 700 and a coupled battery.

Updating of Firmware:

Before the battery system with the BMS 700 is put into service, itsfirmware is loaded. Also, from time to time, improvements to thefirmware can be made. Loading and updating firmware can be done througha data port, such as the USB port 216 or wirelessly via the wirelesscircuitry 220.

GPS Locating Circuitry:

The GPS circuitry 224 allows a vehicle's location and travel routes tobe tracked and monitored. This information, combined with wirelesscommunication can allow the vehicle's location to be reported to aremote location away from the vehicle when the battery system happens tobe lost, located in a stolen vehicle, or has some other need to retrieveits global coordinates.

User Initiated Control:

The BMS 700 can also provide for user-initiated isolation of the battery705 from the system (e.g., from an electrical system or other loadsource) as well as user-initiated re-connection of the battery 705 tothe system. In one embodiment, the user can shut down the BMS 700 toperform the isolation. For example, the user can initiate isolationmanually with a reset button (e.g., the reset button 228 acting as atoggle switch or another button) or remotely with a mobile device orother remote control device. This also allows the user to shut down theengine remotely in the case, for example, the vehicle is being usedwithout proper authorization or has a hazardous condition (e.g., is onfire) and needs to be shut down. The battery 705 may also be isolatedfrom the system by proximity of a paired electronic or mobile device,such as a cell phone using a certain setting. Accordingly, variousembodiments allow for putting the battery 705 in isolation (or takingthe battery out of isolation) depending on the situation and userpreference.

For example, a user may want to trigger isolation (or return fromisolation) to perform any of the following functions:

(1) It is common in the trucking industry for vehicles to be stolenalong with any cargo. Accordingly, the user may want to intentionallyprevent the passing of high current (e.g., sufficient current to start avehicle) by placing the BMS 700 into an anti-theft or “locked” mode,when the user is away from the vehicle or plans to leave the vehicle.The BMS 700 can go into locked mode in response to a deactivation signalor other indicator.

In one embodiment, the user can put the BMS 700 into locked mode througha smart phone application that communicates through the Internet andwith the wireless circuitry 220, for example. Alternatively, oradditionally, the microcontroller 209 can track a location of the userthrough the user's smart phone in comparison with the location of thevehicle (through the GPS circuitry 224), and be pre-programmed to putthe BMS 700 in locked mode after the user has passed a certain distancefrom the vehicle. Similarly, the microcontroller 209 can bring the BMS700 out of locked mode when the user returns within that distance of thevehicle.

In another embodiment, the wireless circuitry 220 includes near-fieldcommunication capability (such as Bluetooth® by the Bluetooth® specialinterest group) and can sense when the user leaves the vicinity of thevehicle. The microcontroller 209, operatively coupled to the wirelesscircuitry 220, can then detect the user has left the vehicle and bepre-programmed to place the BMS 700 into locked mode. To put the BMS 700back into operation mode upon return to the vehicle, the wirelesscircuitry 220 detects that the user is back in range, and makes the BMS700 fully operational with high current capability.

When in locked mode, the microcontroller 209 can detect and prevent thepassing of high current. By intentionally isolating the battery from thesystem, the vehicle cannot be started. In locked mode, for example, theBMS 700 can allow a low specified number of amps to be drawn from thebattery to allow for continuous functioning of basic appliances such asa clock, a radio, security features, and the like. In locked mode,however, the BMS 700 can detect a sudden high current surge (through astart attempt) and isolate the battery. The BMS 700 can also alert theuser through one of the communication interfaces when such an eventoccurs. When the user returns to the vehicle, the BMS 700 can bereactivated such as discussed above, which reconnects the battery 705 tothe electrical system of the vehicle. Isolation and re-connection canadditionally be protected by a passcode.

(2) The user may want to access the reserve power in the battery 705. Todo the user can provide a reset command, for example, by way of a resetbutton on the battery 705 or a remote reset that can be sent via amobile application or the like, wirelessly.

(3) Also, if for some reason the BMS 700 has been isolated the battery705 from the load source due to a harmful condition, and the conditionhas been repaired or resolved, the BMS 700 can then be reactivated. Forexample, the BMS 700 can be reactivated in response to sensing theproximity of a remote device, such as a mobile electronic device of thelike.

Remote display of the BMS 700 status and other logged data may beprovided to a remote device, such as on a mobile device or remotelyoperating computing device. A remote display has the advantage of nothaving to be at the battery to see its status and read data from thebattery. For example, a fleet manager could obtain all the data from thebatteries in the fleet at a single location, without having to go toeach vehicle.

The status display can be as simple as an LED display 230, or other morecomplex display types. This allows the user to observe the statusdirectly on the battery 705.

Power Savings

The BMS 700 may be designed to save power when not in operation. Duringan event, such as turning on a vehicle, powering up a load source,detecting a short circuit or a voltage or current spike, for example,the BMS 700 can be in full power mode. When full functionality of theBMS 700 is not needed, the BMS 700 can go into one of three lower powerstates as follows.

Sleep Mode:

The BMS 700 may spend most of the time in this mode in which the BMS isoperational, but draws little current and has little energy leakage. Thesleep mode may include when the Hall Effect sensors 210 a and 210 b areturned off because they are not needed, as previously explained.

Hibernation Mode:

The BMS 700 can go into hibernation mode when the current consumptionfrom the battery 705 is reduced by a factor on the order of a hundredtimes. In other words, current consumption is much less than wouldotherwise be consumed. In one embodiment, both the Hall Effect sensors210 a and 210 b and the microcontroller 209 are powered off duringhibernation mode. Hibernation mode can be entered at times other thanafter detecting a critical voltage threshold. For example, afterdetecting a period of non-use of the battery 705 by the load source, andto preserve energy of battery 705, the BMS 700 can enter hibernationmode.

Low Power State:

The BMS 700 can enter a low power state when the microcontroller 209powers down one or more of the auxiliary circuitry on the circuit board200, and puts itself into an ultra-low power state. The microcontroller209 can also be activated periodically to monitor vital signs or can beactivated when an event occurs that requires the BMS 700 take action inresponse to the event.

The above-disclosed subject matter is to be considered illustrative, andnot restrictive, and the appended claims are intended to cover all suchmodifications, enhancements, and other embodiments, which fall withinthe true spirit and scope of the present disclosure. Thus, to themaximum extent allowed by law, the scope of the present embodiments areto be determined by the broadest permissible interpretation of thefollowing claims and their equivalents, and shall not be restricted orlimited by the foregoing detailed description. While various embodimentshave been described, it will be apparent to those of ordinary skill inthe art that many more embodiments and implementations are possiblewithin the scope of the above detailed description. Accordingly, theembodiments are not to be restricted except in light of the attachedclaims and their equivalents.

What is claimed is:
 1. An apparatus comprising: an isolation circuitryincluding multiple, transistor-based switches arranged electrically inparallel to isolate a battery from a load source, wherein the battery iscapable of providing high levels of current; a first buss bar to whichfirst pins of the multiple switches are connected, wherein the firstbuss bar is to be connected to the battery; a second buss bar to whichsecond pins of the multiple switches are connected, wherein the secondbuss bar is to be connected to the load source; and a microcontrollerprogrammed to control the multiple switches substantially simultaneouslyto isolate the battery from the load source upon detecting apredetermined condition.
 2. The apparatus of claim 1, further comprisinga heat-conducting bar made of a heat-conducting metal and thermallycoupled to the multiple switches, to equalize a temperature across themultiple switches.
 3. The apparatus of claim 1, further comprising: aswitching driver circuit operatively coupled to the microcontroller andto turn on and off the multiple switches responsive to signals from themicrocontroller; and a plurality of metal traces connecting gates of themultiple switches to the switching driver circuit that are of equallength, such that a signal from the switching driver circuit arrives atthe multiple switches at substantially the same time.
 4. The apparatusof claim 1, wherein the multiple switches are arranged in a firstsubarray and a second subarray, wherein a number of the multipleswitches in the first subarray are equal to those in the secondsubarray.
 5. The apparatus of claim 4, wherein the first buss bar andthe second buss bar each include a first conductive path and a secondconductive path that connect, wherein the multiple switches of the firstsubarray are located in a line along an edge of the first conductivepath and the multiple switches of the second subarray are located in aline along an edge of the second conductive path.
 6. The apparatus ofclaim 5, wherein a first switch in the first subarray and a first switchin the second subarray are located so as to be equidistant from the loadsource along, respectively, the first buss bar and the second buss barin order to synchronize a time for current to arrive at each of thefirst switches.
 7. The apparatus of claim 5, further comprising: acurrent measuring circuit to: determine a first current of the firstconductive path; determine a second current of the second conductivepath; and notify the microcontroller of the first current and the secondcurrent; and wherein the microcontroller is further to generate an alertindicative of the first current and the second current differing beyonda pre-defined threshold amount indicative of degradation of one or moreof the multiple switches.
 8. The apparatus of claim 1, wherein thepredetermined condition comprises one of: a short circuit in the loadsource, overheating of the battery, overheating of the isolationcircuitry, a low-voltage threshold of the battery, or a user-initiatedshut off.
 9. The apparatus of claim 1, further comprising a metal oxidevaristor (MOV) coupled to the first buss bar or to the second buss barin parallel with the multiple switches, to provide voltage suppressionby shunting current caused by high voltages away from the multipleswitches.
 10. The apparatus of claim 1, further comprising: a printedcircuit board located between the first buss bar and the second buss barand to which is attached the microcontroller; and a thermal sensorattached to the printed circuit board and operatively coupled to themicrocontroller, wherein the thermal sensor is to: measure a temperaturelevel of the second buss bar; and responsive to detecting a temperatureabove a pre-determined threshold temperature, send a signal as anover-temperature indicator to the microcontroller; and wherein themicrocontroller is to switch off the multiple switches responsive to thesignal.
 11. The apparatus of claim 1, further comprising measurementcircuitry to: measure, to a high level of accuracy, a resistance of onebuss bar selected from the first buss bar and the second buss bar;determine a current level through the one buss bar in view of a voltagemeasured across the one buss bar and the resistance of the one buss bar;and detect a high current surge condition in view of the current levelbeing over a predetermined threshold high current.
 12. The apparatus ofclaim 11, wherein the load source is a vehicle, and wherein themeasurement circuitry is further to distinguish the high current surgecondition in view of the current level being below the predeterminedthreshold high current.
 13. An apparatus comprising: an isolationcircuitry including multiple, transistor-based switches arrangedelectrically in parallel to isolate a battery from a load source,wherein the battery is capable of providing high levels of current of atleast 400 amperes; a switching driver circuit operatively coupled to theisolation circuitry such as to switch off the multiple switchessimultaneously; and a microcontroller operatively coupled to theswitching driver circuit, wherein the microcontroller is to direct theswitching driver circuit to turn off the multiple switches responsive todetecting a predetermined condition.
 14. The apparatus of claim 13,wherein the multiple switches are arranged in a first subarray and asecond subarray, wherein a number of the multiple switches in the firstsubarray are equal to those in the second subarray, wherein a firstswitch in the first subarray and a first switch in the second subarrayare located so as to be equidistant from the load source.
 15. Theapparatus of claim 13, wherein the multiple switches operate within arange of switching rates, and wherein the switching driver circuit is toswitch off the multiple switches at a slowest rate within the range ofswitching rates without exceeding a maximum allowable power dissipationcaused by switching.
 16. The apparatus of claim 13, wherein the batteryincludes a plurality of banks of cells, further comprising ananalog-to-digital converter (ADC) to measure a voltage of a bank of theplurality of banks of cells and to send the voltage to themicrocontroller, wherein the microcontroller is further to: determine anumber of charge cycles in which the voltage has cycled between aspecified first voltage and a specified second voltage; determine anamount of time in which the bank is at a critical voltage level thatdepends on a type of the battery; and generate an alert indicative ofdegradation of the bank responsive to passing a threshold number ofcharge cycles and a pre-defined amount of time at the critical voltage.17. The apparatus of claim 13, wherein the predetermined conditioncomprises a high pre-set current level over a short period of time,wherein an amount of the high pre-set current level depends on the loadsource.
 18. The apparatus of claim 13, wherein the predeterminedcondition comprises a reserve voltage below which the microcontroller isto generate an alert to reset the battery in order to access reservecapacity.
 19. The apparatus of claim 13, wherein the predeterminedcondition comprises a low-voltage threshold below which themicrocontroller is further to: shut off the multiple switches to protectthe battery from over-discharging; and require charging the batteryabove the low-voltage threshold before accepting a reset to begindrawing on the battery again.
 20. The apparatus of claim 13, wherein themicrocontroller is further to: retrieve a critical low voltage for thebattery; track an amount of time at which the battery is at or below thecritical low voltage; responsive to the battery being at or below thecritical low voltage for a predetermined minimum period of time, causethe battery to enter a hibernation mode of extremely low currentconsumption when compared with normal operation of the battery; andrequire recharging the battery above the critical low voltage beforeaccepting a reset to again draw power from the battery.
 21. Theapparatus of claim 13, wherein the load source is a vehicle, and whereinthe microcontroller is further to: restrict amperes available to thevehicle, as drawn through the multiple switches, to an amountinsufficient to turn on the vehicle; and reverse the restriction inamperes responsive to receiving a signal indicating presence of anauthorized operator.
 22. An apparatus comprising: an isolation circuitryincluding multiple, transistor-based switches arranged electrically inparallel on a circuit board, wherein the isolation circuitry is toisolate a load source from a battery that is capable of providing highlevels of current; a surge detection circuit including an operationamplifier to detect a surge in current by measuring a voltage differencebetween source and drain of a subset of the multiple switches; a surgemeasuring circuit to measure a magnetic field and to determine a currentlevel of the surge in current; and a microcontroller operatively coupledto the surge detection circuit and the surge measuring circuit, whereinthe microcontroller is to: receive a first signal from the surgedetection circuit, wherein the first signal is indicative of detectingthe surge in current; turn on the surge measuring circuit responsive tothe first signal; receive the current level of the surge from the surgemeasuring circuit; and send a second signal to switch off the multipleswitches responsive to determining that the current level is above apre-defined threshold current level indicating a short circuit.
 23. Theapparatus of claim 22, wherein the surge measuring circuit includes aHall Effect sensor attached to the circuit board with which to measurethe magnetic field.
 24. The apparatus of claim 22, wherein the surgedetection circuit further includes a digital-to-analog (ADC) circuit togenerate the first signal responsive to the surge detection circuitdetecting the surge in current.
 25. The apparatus of claim 22, whereinthe microcontroller is further to set the pre-defined threshold currentlevel according to a size of the battery or a size of the load source.